A Phnom Penh municipal court has sentenced a university student to 18 months in prison for a Facebook posting that calls for revolution.

Tuesday's ruling by Judge Heng Sokna shocked supporters and family members of Kong Raiya, 24, who prior to his verdict hearing said he thought he would be released.

The first-year student from Khemarak University was arrested last August on charges of incitement after posting a Facebook message calling on Cambodians to join him in a "color revolution" to change the government.

Cambodia’s constitution protects free speech in theory, but in practice, the regime of Prime Minister Hun Sen is highly sensitive to dissent. The courts, widely criticized as politically biased, have shown a willingness to prosecute for criminal charges related to public speech, including for incitement and defamation, charges that most often fall on government critics.

Kong Raiya’s father, Kong Taing, called the sentencing "harsh" and said his son had not actually sought to orchestrate a revolution against the government. "He should not have been convicted for such a long imprisonment, because this is a matter of an expression of opinion," he said, adding that his family plans to appeal the case.

Student leaders from Khemarak University submitted a petition to Prime Minister Hun Sen calling for Kong Raiya’s release, but have not received a response.

Am Sam Ath, a senior investigator with Phnom Penh-based rights group Licadho who observed Tuesday’s hearing, said the judge’s decision was unwarranted, especially because the Facebook post was not a credible threat to national security.

During his trial in February, Kong Raiya told the judge his understanding of a color revolution was that it meant peaceful gatherings and non-violent protests. In his Facebook post, he said, "Does anyone dare (sic) to launch a color revolution with me? Some day in the future, I will launch a color revolution in order to change the regime running Cambodian society; even if I am sent to prison or die, I am determined to do it."